Space discharge device having grid of varying electron transparency



June ML 1951 MONTANI SPACE DISCHARGE DEVICE HAVING GRID OF VARYING'ELECTRON TRANSPARENCY Filed Nov'. 28, 1947 ....15 om .O Q: o...

INVENTOR. ANGELO MONTANI M @w lll 5? MI.. ND mm. 1.". Iliff- 'fill k w dW w m N P ATTORNEY Patented June 19, 1951 SPACE DISCHARGE DEVICE HAVINGGRID F VARYING ELECTRON TRANSPARENCY Angelo Montani, Woodhaven, N. Y.,assigner to Automatic Electric Laboratories, Inc., Chicago, Ill., acorporation of Delaware Application November 28, 1947, Serial No.788,490

(Cl. Z50-27) 3 Claims.

The present invention relates in general to circuit arrangementsutilizing space discharge devices of the electron beam type.

It is an object of the present invention to provide a circuit; includinga space discharge device of the electron beam type in which the normalparameters, such as the Mu and Gm etc., of the tube may be varied at thewill of the operator.

Another object of the invention is the provision of a circuit includinga space discharge device of the electron beam type so arranged as toperform the functions of an FM discriminator and limiter combined.

Other objects and features of the invention will become apparent upon afurther perusal of the specification.

Briefly these objects are accomplished by providing a special controlgrid and a collecting plate in a tube structure similar to aconventional cathode ray tube. The control grid is so constructed as tohave a variable electron transparency, the grid mesh being the leastdense in the middle of the grid in the region through which theundeviated electron beam will pass,

and gradually becoming more dense on either side of the middle regionand finally becoming opaque at each end of the grid.l The position ofthe beam of electrons on the grid is determined by means of a suitablevoltage applied to a pair of deilecting plates. The electrontransparency ofthe grid region through which the electron beam is causedto pass obviously determines the characteristics of the tube. It isapparent then that the tube characteristics may be varied by causing theelectron beam to pass through different grid regions under control ofthe voltage applied to the deecting plates.

When used as an FM discriminator the deflecting plates are connected tothe last IF stage of the receiver. The electron beam will now be causedto oscillate back and forth across the grid, the angle through which thebeam swings will be proportional to the frequency deviation of the FMsignal. If the electron beam swings through a small arc, that isconfined mostly to the middle region of the grid where the mesh is theleast dense, the average plate current will be the greatest. As the arcthrough which the electron beam swings increases, the beam encountersthe more dense regions of the grid and the average plate currentconsequently decreases until a minimum average plate current is reachedwhen the arc through which the lbeam swings is so great as to cause thebeam to swing over the opaque regions at either end of the grid. Thusthe tube produces an average plate current which is a function of thefrequency deviation which of course is the function and purpose of an FMdiscriminator.

The invention will be better understood from the following descriptionwhen taken in conjunction with the drawings in which:

Fig. 1 discloses one form of the invention in a circuit for use as acombined FM discriminator and limiter.

Fig. 2 shows a set of analytical curves for use in explaining theoperation of the device.

Fig. 3 shows an alternative method of energizing the deflecting platesby a direct current source to thereby lock the beam in any desiredposition.

Referring to Fig. 1 of the drawing, there is shown a cathode ray tubehaving the conventional heater l, cathode 2, and beam forming electrodes3, 4, and 5 all of which are energized by a suitable battery I5 or thelike. The pencil like electron beam, indicated by the broken line '1,passes between a pair of electrostatic deflecting electrodes 6 which arepositioned on op-` posite sides of the beam axis. It is to be understoodthat the equivalent magnetic deflecting coils or other suitable meansmay be substituted for the electrostatic deflecting electrodes, ifdesired. The electron beam 'l is caused to scan a rectilinear path alongvarying portions of control grid 8. Grid 8 is constructed so as to havea varying mesh density along its length as is shown. The solid portionsIl at either end of grid 8 are opaque to the electron beam and ac.tually become collecting plates. Grid 8 is energized through resistancel2 by a suitable battery I3 or the like. Electrode 9 is a collectingplate and is energized by battery l5 through re. sistance H across whichthe audio output voltage is developed. across resistance l l may beresistance coupled 'or capacitance coupled, as is shown, to the nextstage of audio equipment.

The deecting plates 6 are connected to the output from the last IF stageof the receiver, the beam of electrons thus being deviated from itsnormal path in accordance with the voltage developed by this stage. TheIF transformer I6 is not tuned to the center, or unmodulated, car-4 rierbeat frequency as is normally the case but is rather tuned to the lowestbeat frequencyoca curring when the FM carrier is modulated. Actually theIF transformer i6 may be `tuned below this frequency or it may be Atunedabove The output voltage developedthe highest beat frequency to whichthe IF signal will deviate when the carrier is 100% modulated and thedevice will function satisfactorily as a discriminator.

Consider now the operation of the device of Fig. 1 in conjunction withthe analytical curves of Fig. 2. The curve on the right hand side ofFig. 2 shows the FM modulating signal which is causing the FM carrierfrequency, indicated at g, to deviate between the points f and h, fbeingthe lowest frequency and h being the highest. The IF transformer I6 istuned to the beat frequency occurring When the carrier frequency is atf, it being assumed that the carrier is 100% modulated. At the point aon the modulating signal, the voltage induced on the deflecting plates 6by the IF transformer I6 will be a median value and the electron beamwill scan all of the sparsely meshed region of grid 8 and part of thedenser regions. The average plate current for this condition will besome value such as d in the left hand curve of Fig. 2. As the modulatingvoltage increases to point b causing the carrier frequency to increaseto point h, the voltage developed across transformer i6 decreasesbecause the beat frequency is deviating farther away from the resonantfrequency of transformer IS. Under this condition the beam will notswing as far as at point a. and will consequently scan just over thecenter region of grid 8 thus producing an in-` creased average platecurrent sueli as is indicated at point b in theleft hand curve of Fig.2. The analysis for the point C is the same as for point a resulting inthe decrease of the average, plate current to point C. At point d thecarrier frequency has decreased to the point f and the beat frequencywill be at the resonant frequency of transformer I6 hence the voltage onthe defiecting plates 6 will be a maximum. Under this condition the beamwill make its maximum swing, scanning all of the meshed portions of grid8 just up to the opaque portions Il. The beam thus Scans the more denseregions of grid 8 resulting in a decrease in the average plate currentto a point indicated at d. The analysis for point e is again the same asfor point a. resulting in an increase of the average plate current tothe point e'.

It is clear from the foregoing analysis that the average plate currentflowing through resistance Il varies in a manner conforming to thesignal modulating the FM carrier. The variations in the electrontransparency of grid 8 may be made to conform with the selectivity curveof the last IF. stage or in fact may be made to conform with any desiredlaw.

It will be noted that grid 8 is slightly positive by virtue of batteryI3 thus a current will flow in the grid circuit developing a voltageacross resistance I2. This voltage is filtered at I4 and connected to apreceding IF amplifier stage. The purpose of this arrangement is tocause the tube of Fig. 1 to act as a limiter as well as a discriminator.The filtered voltage emanating from filter M, when the beam is scanningbetween the solid portion I1 of grid 8, will not vary appreciably but ifa disturbing AM signal should become superimposed upon the FM signal thebeam would scan over the solid portions l1, resulting in a largeincrease in the grid current and an increase in the filtered voltage.This voltage may be utilized in a preceding IF amplifier stage formomentarily reducing the gain in any well known manner. Thus anyunwanted AM signal will be ineffective to cause distortion inthe audi@ 4output by reason of the feedback from the grid circuit of the tube inFig. 1.

The tube of Fig. 1 may also be used as a triode. The deflecting voltageapplied to plates 6 in this case might come from any suitable directcurrent source such las for example is shown in Fig. 3. In Fig. 3 thedeflecting plates 6 are energized by means of the potentiometer 3|connected across battery 30. This arrangement enables the operator toposition the beam through any desired region of grid 8 to thereby choosethe operating characteristics of the tube. The grid circuit would thenbe connected in a suitable manner for which the tube as a triode is tobe used.

The tube may also be used as a vacuum tube voltmeter, the voltage to bemeasured being applied to the delecting plates and the plate currentreading being calibrated to read voltage.

While what is now considered to be the preferred form of the inventionhas been illustrated, it is to be understood that numerous modificationsmay be incorporated therein without departing from the true spirit andscope of the invention as defined in the subjoined claims.

What is claimed is:

1. In a frequency modulation discriminator system, means for developingand projecting a beam of electrons in a given path, a grid located insaid path for screening said projected beam, said grid having a mesh ofvarying electron transparency ranging from a region of relativelymaximum transparency through a region of relatively minimum transparencyto and including an opaque region, a circuit connected to said grid,means for impressing a potential upon said grid to cause a current flowin said circuit, means for filtering a potential from said current flow,means for causing said beam to scan said grid, control means responsiveto received frequency signals for controlling said fourth mentionedmeans to cause said beam to variably scan only said transparent regionsof said grid, the amount of said current flow varying only in relativelysmall values responsive to said variable scanning of said transparentregions, said filtered potential varying in corresponding small valuesresponsive to said value Variations in said current ow, said controlmeans responsive to received frequency signals and a receivedinterfering signal for controlling said fourtn mentioned means to causesaid beam to scan said opaque region of said grid, said current flowrising to a relatively high value responsive to said scanning of saidopaque region, said filtered potential rising to corresponding highvalue responsive to said high value rise in said current flow.

2. In a frequency modulation discriminator system as claimed in claim lwherein said received frequency signals consist of receivedfrequencymodulated intermediate frequency signals, and wherein saidreceived interfering signal consists of a received strayamplitude-modulated signal superimposed on one of'said receivedfrequencymodulated intermediate frequency signals.

3. In a frequency modulation discriminator system, means for developingand projecting a beam of electrons in a given path, a collecting platelocated in said path, an output circuit connected to said plate, a gridlocated in said path for screening said beam projected towards saidplate, said grid having a mesh of varying electron transparency rangingfrom a region-of relatively maximum transparency through a region ofrelatively minimum transparency to and including an opaquedV region, agrid circuit connected to said grid, means for impressing a potenti-alupon said grid to cause a current ilow in said grid circuit, means forltering a potential from said current iloW and for extending saidfiltered potential to an intermediate frequency amplifier stage, meansfor causing said beam to scan said grid, control means responsive toreceived frequency signals for controlling said fourth mentioned meansto cause said beam to variably scan only said transparent regions ofsaid grid, electrons of said beam impinging upon said plate responsiveto said variable scanning of said transparent regions to cause a currentiiow in said output circuit, the number of electrons impinging upon saidplate varying as the amplitude of said variable scanning of saidtransparent regions increases and decreases, the amount of said currentflow in said output circuit varying responsive to said variance in thenumber of said impinging electrons, the potential of said current ilowin said output circuit correspondingly varying responsive to saidvariations in the amount of said current flow .in said output circuit,the amount of said cur- 'rent flow in said grid circuit varying only inrelatively small values responsive to said variable scanning of saidtransparent regions, said ltered potential varying in correspondingsmall values responsive to said value variations in said current ilow insaid grid circuit, said control means responsive to received frequencysignals and a received interfering signal for controlling said fourthmentioned means to cause said beam to scan said opaque region of saidgrid, said current ow in said grid circuit rising to a relatively highvalue responsive to said scanning of said opaque region, said filteredpotential rising to corresponding high value responsive to said highvalue rise in said current flow in said grid circuit, said high valuerise in said filtered potential causing a reduction in the gain of saidampliier stage to control the intensity of said beam in a sense torender said potential of said current flow in said output circuitindependent of said scanning of said opaque region of said grid.

ANGELO MONTANI.

REFERENCES CITED The following references are of record in the le ofthis patent:

UNITED STATES PATENTS Number Name Date 1,757,345 Strobel May 6, 19301,839,904 Sutherlin Jan. 5, 1932 2,048,224 Snow July 21, 1936 2,075,202Jonker Mar. 30, 1937 2,173,193 Zworykin Sept. 19, 1939 2,408,702 SziklaiOct. 1, 1946

